Track soundproofing arrangement

ABSTRACT

A noise control device for tracks ( 1 ) comprising sound-absorbing slabs ( 3 ) mounted at the rails ( 2 ) of the track ( 1 ), the slabs being supported on the rails ( 2 ) via elastic sections ( 5 ) and self-supportingly bridging the space between the rails ( 2 ). To improve silencing of the slabs ( 3 ) it is provided for the slabs ( 3 ) to be comprised of particles ( 9 ) of porous lightweight building material, which are combined by a binder. The slabs ( 3 ) have an embedded reinforcement ( 11 ). Advantageously, also silencing cavity resonators ( 14 ) are formed in the slabs ( 3 ). A special embodiment provides for the space between the rails ( 2 ) of a track to be bridged by slab parts ( 3   a,    3   b ) arranged in pairs which are supported on each other at their rims ( 26, 27 ) facing each other.

BACKGROUND OF THE INVENTION

The invention relates to a noise control device for tracks comprisingsound absorbing slabs mounted at the rails of the track, the slabs beingsupported on the rails via elastic sections, the slabs arranged betweenthe rails self-supportingly bridging the space between the rails.Furthermore, the invention relates to sound-absorbing slabs for such anoise control device.

In a noise control device of the above-mentioned type known from DE 3602 313 A1, the slabs arranged between the rails of the track consist ofthree plies or layers supported on the rail base, on the rail web and onthe lower side of the rail head via elastic sections. The upper layerconsists of a passable woven steel wire whose rim is glued, welded orvulcanized into the section. The middle layer forms a sound absorptionlayer and consists of glass wool or rock wool. This sound absorptionlayer rests on the lower layer which is a perforated wall or grate andis supported in a recess of the section in the region of the rail base.According to a further embodiment, the slabs are also arranged on therail outer side and upwardly angled at their ends so as to form alateral noise control wall. Such slabs of mineral wool do providesufficient silencing at high frequencies, yet at low frequencies theirsilencing is insufficient. Furthermore, this construction has thedisadvantage that under higher and repeated loads, the passableperforated layer of woven steel wire may become detached from itsanchoring in the sections so that the sound absorbing layer arrangedtherebelow may become damaged. Moreover, the dust penetrating theperforated layer may deposit on the upper side of the sound absorptionlayer and thus the silencing effect may increasingly deteriorate.

From NL-A-9400910 a noise control device for tracks is known, in whichslabs made of wood fiber concrete are arranged between the rails of thetrack, which slabs rest on the sleepers of the track and laterally abuton the rails with elastic strips interposed. There is no self-supportingmounting of these slabs.

SUMMARY OF THE INVENTION

The invention has as its object to provide a noise control device fortracks comprising sound absorbing slabs which have good sound absorptionor silencing over the entire range of frequencies essential for thenoise levels of rail traffic, wherein also a lasting mechanical strengthof the device is to be ensured.

In the noise control device of the initially defined type, according tothe invention this object is achieved in that the slabs are comprised ofparticles of porous lightweight building material combined by a binderand that the slabs have an embedded reinforcement and are arrangedwithout cover. By this design, the aforementioned objects can be metwell. The airborne sound particularly arising from the wheels of a railvehicle and from the rails is absorbed at the surface of the slabs bythe pores of the particles, and even when a structure having fine gapsbetween the particles is chosen, the sound can penetrate more deeplyinto the slab via gaps or channels present between the particles so asto be gradually completely silenced there. By reinforcing the slabs,also their passability is ensured.

To further improve the sound absorption properties of the slabs, it isadvantageously provided that the upper side of the slabs is structured,and even better results being obtainable if the structuring isirregular.

Preferably, the upper side of the slabs is provided with ribs extendingin parallel to the rails, resulting in a structuring which is easy to beconstructed.

It is also advantageous if the ribs have a trapezoidal cross-section,since thus obliquely incident sound waves can be better absorbed.

An additional improvement of the sound absorption properties of theslabs is obtained in that cavity resonators having tubular soundapertures directed to the upper side of the slabs are formed in theslabs. In this manner, certain frequency ranges of the impacting soundwaves purposefully can be better absorbed.

To increase the silencing effect of the cavity resonators, it issuitable if the walls of the cavity resonators and their sound aperturesare provided with a silencing structuring, and/or if the walls of thecavity resonators and their tubular sound apertures are provided with asilencing layer.

According to a structurally simple embodiment it is provided that thecavities forming the cavity resonators are designed such that they widendownwardly and are open, and are covered by a lower plate. In adifferent, also structurally simple embodiment it is provided that thecavities forming the cavity resonators are designed such that they widendownwardly and are open and form a resonance cavity together with therail bedding.

In practice, it has proven to be suitable if the dampened resonancefrequency of the cavity resonators lies within a frequency range of from150 to 1,000 Hz, preferably between 500 and 1,000 Hz.

Within the scope of the invention also a special embodiment is providedin which the installation and removal of the slabs to be providedbetween the two rails of a track can be effected in a very simplemanner. This embodiment of the noise control device is characterized inthat the space present between the two rails of a track is bridged withslab parts arranged in pairs, each engaging by at least one carrying ribin the fishing surfaces of the rails, the slab parts of each slab pairbeing supported on each other at their facing rims, carrying portionsand resting portions following each other in meander-like alternatingfashion at each slab part along the rim facing the other slab part, thecarrying portions being formed by indentations originating from the slabupper side and extending as far as to the rim facing the other slabpart, upwardly directed indentations originating from the slab lowerside being formed below the resting portions, which indentations areshaped complementary to the indentations of the carrying portions, andthat the resting portions of the one slab part rest on the carryingportions of the other slab part, and that the resting portions of theother slab part rest on the carrying portions of the one slab part Withslab parts in a folded-up position, the hinge-like assembled zones ofthe slab parts of each slab pair can be simply nested in each other,whereupon the slab parts can be inserted between the rails without anyproblem by levelling the slab pair, and neither will the slab parts bepressed apart under the action of loads.

A preferred type of the last-mentioned embodiment, which ischaracterized in that at those surfaces on which the slab parts of oneslab pair contact each other, projections and indentations shapedcomplementary to the projections are formed, the projections latchinglyengaging in the indentations for a mutual latching of the slab parts,has the advantage that the positive fit of the slab parts of a slab pairwill be ensured over very long periods of time even if unfavorablevibrations act on the slab parts.

In terms of as simple an insertion procedure as possible of the slabparts between the rails, which is to be effected with little expenditureof force, and in terms of a possible simple removal of the slab parts itis advantageous if it is provided that the carrying surfaces provided inthe carrying portions, starting from the rim facing the other slab partof the slab pair, at first rise steeply, starting from the slab lowerside, and then flatten. There, it is furthermore suitable and alsoadvantageous for ensuring a stable positive fit of the slab parts overextended periods of time in their installed state, if it is providedthat the carrying surfaces provided in the carrying portions have acrowned shape, which shape inhibits a mutual movement of these slabs inthe direction of the slab plane in the levelled position of the slabparts of the respective slab pair. Such a crowned shape may be formed onone slab part by a surface portion originating from the rim facing theother slab part of the slab pair, which surface portion extends awayfrom the lower side of the slab, and a consecutive surface portion whichextends towards the lower side of the slab. If with such a design of theslab parts it is desired to provide for an additional latching, it isadvantageous if the latter is designed such that downwardly extendingprojections are provided at the front rims of the resting portions, andindentations complementary to these projections are provided on thecarrying surfaces of the carrying portions.

Particularly suitable for the course of the levelling procedure duringthe installation of the slab parts and for attaining as stable aposition as possible of the two slab parts of a slab pair relative toeach other in the installed state is an embodiment which ischaracterized in that the crowned carrying surfaces are shaped like atoothing which allows for a sliding movement or rolling movement of thefacing carrying surfaces and resting surfaces one on the other up to alevelled position of the slab parts of the respective slab pair, andwhich in the levelled position of these slab parts locks against amovement of these slab parts relative to each other.

Furthermore, there results a geometry favourable for the assembly of theslab parts of a slab pair and for the subsequent relative movement ofthese two slab parts during the installation procedure of the slabparts, if it is provided for the slab parts to be rounded at theirfacing rims from the plate lower side upwards, the radius of curvaturebeing equally dimensioned or smaller than the distance between theserims and the rail-side rims of the slab parts. For as simple an assemblyas possible of the slab parts of a slab pair it is advantageous if it isprovided for the two slab parts of a slab pair to abut each other at theslab lower side approximately along a straight line. If, however, ashigh a carrying capacity as possible of the slab pair is to be attained,it is suitable if it is provided for the two slab parts of a slab pairto abut each other at the slab lower side so as to engage into eachother in meander-like fashion.

With a view to the construction of the slab parts themselves it issuitable if the reinforcement provided in the slab parts extends overthe slab area and reaches both into the carrying portions and restingportions and into the carrying ribs. It is also suitable if it isprovided that an elastic and/or shock-braking insert or coating isprovided between the carrying surfaces provided on the carrying portionsand the resting surfaces provided on the resting portions.

A sound-absorbing slab according to the invention is characterized inthat the slab is comprised of particles of porous lightweight buildingmaterial combined by a binder, that the slab has an embeddedreinforcement, and that in the slab cavity resonators are formed withtubular sound apertures oriented towards the one large surface of theslab, which large surface is to form the upper side when installing theslab in the track. Therein, it is advantageous if the cavities formingthe cavity resonators are designed to widen and to be open towards thatlarge surface which is located at that side of the slab that faces awayfrom the tubular sound apertures. Therein, a further development ischaracterized in that the cavities forming the cavity resonators arecovered by a lower plate at the side facing away from the tubular soundapertures. Embodiments of a slab configured according to the inventionwhich are provided for the previously mentioned configuration comprisingslab parts to be assembled to a slab pair are characterized in that theslab is comprised of particles of porous lightweight building materialcombined by a binder, that the slab has an embedded reinforcement, thatthe slab on one rim side is provided with a carrying rib for engagementin the fishing surfaces of rails, and, at the rim side opposite thiscarrying rib, comprises meander-like successive carrying portions andresting portions, the carrying portions being formed by indentationsoriginating from the slab upper side and extending as far as to the rim,upwardly directed indentations originating from the slab lower sidebeing formed below the resting portions and being shaped complementaryto the indentations of the carrying portions. Preferably, it is thereprovided that in the slab cavity resonators are formed with tubularsound apertures oriented towards the one large surface of the slab,which large surface is to form the upper side when installing the slabin the track. Here, it is furthermore suitable if the reinforcementprovided in the slab extends over the entire slab area and into thecarrying portions and into the resting portions as well as into thecarrying rib. If desired, the slabs or the slab parts may also beprovided with a frame extending along the rim and preferably consistingof metal or fiber-reinforced plastic.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be further explained with referenceto the drawings. In the drawings,

FIG. 1 shows a top view onto a track having sound-absorbing slabsarranged between its rails,

FIG. 2 shows a section according to line II—II of FIG. 1,

FIG. 3 shows an embodiment of a slab, in cross-section, and

FIG. 4 shows an enlarged detail of the surface of the slab according toFIG. 2 or 3;

FIG. 5 shows an embodiment of a noise control device which comprisesdivided slab parts, in top view,

FIG. 6 shows this embodiment in a section according to line VI—VI ofFIG. 5,

FIG. 7 shows this embodiment in a section according to line VII—VII ofFIG. 5,

FIG. 8 shows a slab part provided in such a covering, in an axonometricview,

FIG. 9 shows a pair of such slab parts, also in an axonometric view, ina folded-up state while they are being installed,

FIG. 10 shows a modification with respect to the design of the carryingportions and resting portions in a sectional representationcorresponding to that of FIG. 7,

FIG. 11 shows another embodiment of a noise control device comprisingdivided slab parts, in top view,

FIG. 12 shows this embodiment in a section according to line XII—XII ofFIG. 11,

FIG. 13 shows this embodiment in a section according to line XIII—XIIIof FIG. 11,

FIG. 14 shows a slab part provided in a noise control device accordingto FIG. 11, in axonometric view,

FIG. 15 shows a pair of such slab parts in a folded-up state in thecourse of the insertion procedure, also in an axonometric view, and

FIG. 16 shows a modification with respect to the design of the carryingportions and the resting portions of the divided slab parts in asectional representation corresponding to that of FIG. 13.

DETAILED DESCRIPTION OF THE INVENTION

At the track 1 illustrated in FIGS. 1 and 2, sound-absorbing slabs 3 areadjacently arranged between the rails 2 in the longitudinal direction ofthe track. On both of their rims which extend along the rails 2, thegenerally rectangular slabs 3 comprise projecting carrying ribs 4 whichrest on the rail base 6, on the rail web 7 and on the lower side of therail head 8 of the rails 2, with elastic sections 5, e.g. of rubber orelastomer, interposed. The slabs 3 whose surface is represented on anenlarged scale in FIG. 4, are comprised of particles 9 of porouslightweight building material combined by a suitable binder. As thelightweight building material, synthetic material granules, granular orspherical and burnt alumina particles, granular slag particles or thelike burnt natural or synthetically produced materials may, e.g., beused, these particles being punctually connected by means of a suitablesynthetic binder or cement so that small gaps or channels 10 remainwhich allow for a transmission of airborne sound and the drainage ofpenetrating rain or melt water. To provide the slabs 3 with sufficientmechanical strength so as to make the slabs 3 passable, the slabs 3 areprovided with a reinforcement 11, e.g. of steel or of other metals,fiber-reinforced plastic, glass fiber mats or the like. The airbornesound incident on the slabs 3 is absorbed at the surface of the slabs 3by the pores of the particles 9 and can penetrate more deeply into theslab 3 via the gaps or channels 10 remaining between the particles 9 tobe gradually absorbed there. To increase this sound absorption effect,the surface of the slabs 3 can be enlarged by structuring. Thus, e.g.,the upper side 12 of the slabs 3 may be provided with ribs 13 extendingin parallel to the rails 2 and arranged in spaced relationship to eachother, which ribs 13, as is illustrated in FIG. 3, have a trapezoidalcross-section and a height a above the rail head 8 which does not exceeda permissible amount of, e.g., 5 cm. Structuring may also be irregular,e.g. by the distance of the ribs 13 from each other increasing ordecreasing. As the structuring of the upper side 12, e.g. also truncatedcones, truncated pyramids, cylinders, cuboids etc. may be provided,which are arranged either at equal or at varying distances from eachother.

To further increase the previously mentioned sound absorption effect ina broad range of frequencies of the sound level, cavity resonators 14are formed in the slabs 3 in the manner of Helmholtz resonators whosetubular sound apertures 15 are provided at the upper side 12 of theslabs 3. In the embodiment illustrated in FIG. 2, the cavities formingthe cavity resonators 14 are frustoconical and open towards the bottom,the apertures thus formed being covered by a lower plate 16 which is,e.g., glued to the slab 3 to form the cavity resonator 14. It may alsobe advantageous to leave the cavities forming the cavity resonators opentowards the bottom so that they form a resonance cavity together withthe space present between the rail bedding 17 merely schematicallyillustrated by a dot-and-dash line (e.g. sleepers of the track and bedof broken stones or concrete slab substructure) and the lower side ofthe respective slab 3. The cavities forming the cavity resonators 14 mayalso have a shape other than frustoconical, they may e.g. be spherical,cylindrical, pyramidal etc., to achieve a different frequency behaviourat sound absorption. Likewise, the volumes of the cavity resonators 14and the dimensions of the tubular sound apertures may be varied toachieve the desired frequency behaviour or frequency absorptionspectrum, respectively. The tubular sound apertures 15 open, as isillustrated in FIG. 2, at right angles to the upper side 12 of the slab3. As a variation of this arrangement, the tubular sound apertures 15may also end obliquely to the upper side 12 of the slabs 3 so that theycan better receive obliquely incident sound waves.

The slabs 3 with the cavity resonators 14 may be produced in arectangular mould in which positive moulds of the cavity resonators areinserted with attached tube pieces for the sound apertures, whereuponthe mould is filled with the particles 9 and a binder, and the mould isopened after setting of the binder. As the positive moulds, alsopre-fabricated cavity resonators with attached tube pieces as soundapertures may be inserted in the mould which are either comprised of asuitable sound absorbing material or are provided with a layer of soundabsorbing material at their inner surface.

As is illustrated in FIG. 2, sound absorbing slabs having cavityresonators may also be provided on the outer side of the rails 2. Theslab 18 illustrated in dot-and-dash line at the right-hand rail 2 issupported at one end on the rail 2 via an elastic section 5, similar tothe slab 3 arranged between the rails 2, and at the other end it issupported via an elastic strip 19 and fixed by means of a fasteningelement, in particular a screw 20. Slab 21 illustrated also indot-and-dash line at the left-hand rail 2 is supported and fixed in thesame manner as slab 18, yet on its outer side it has an upwardly angledend region so as to form a noise control wall. The two slabs 18, 21 alsoinclude a reinforcement (not illustrated) as well as optionally astructuring in the form of ribs (not illustrated). If desired, the slabsmay also be provided with a frame extending along their rim.

In the embodiment of a noise control device according to the inventionand illustrated in FIGS. 5 to 7, the space 22 present between the tworails 2 of a track 1 is filled or bridged, respectively, bysound-absorbing slab parts 3 a, 3 b arranged in pairs. These slab parts3 a, 3 b comprise carrying ribs 4 engaging in the fishing surfaces 23 ofthe rails 2, and elastic sections 5 of approximately C-shapedcross-section are inserted between the carrying ribs 4 and the rails 2.In this manner, the slab parts 3 a, 3 b are supported on the rail base 6by their carrying ribs 4, are resting laterally against the rail web 7,and upwardly they are held by engagement under the rail head 8. Thecombined slab parts 3 a, 3 b bridge the distance 24 between the rails 2self-supportingly. On each of the slab parts 3 a, 3 b several carryingribs 4 are provided in spaced relationship from each other so as to keepthe fastening elements 25 provided for the rails 2 accessible. However,when choosing different slab dimensions and slab installationarrangements, also just a single carrying rib 4 may be provided on eachslab part.

At their rims 26, 27 facing each other, the slab parts 3 a, 3 b of eachslab pair are supported on each other, each slab pair thus forming anassembled body self-supportingly bridging the distance 24 between therails 2. For this, carrying portions 28 and resting portions 29following each other in meander-like alternating fashion are provided ateach slab part 3 a and 3 b, respectively, along the rims 26 and 27,respectively, facing the other slab part 3 b and 3 a, respectively; thecarrying portions 28 are formed by indentations 30 originating from theslab upper side 12, which indentations extend as far as to the rimfacing the other slab part; below the resting portions 29, upwardlydirected indentations 32 originating from the slab lower side 31 areformed, and the resting portions of the slab part 3 a rest on thecarrying portions of the slab part 3 b, and the resting portions of theslab part 3 b rest on the carrying portions of the slab part 3 a; theindentations 30 are designed to be complementary to the indentations 32,so that the resting surfaces 34 formed by the indentations 32 on theresting portions 29 rest with a substantially snug fit on the carryingsurfaces 33 formed by the indentations 30 on the carrying portions 28.As regards the afore-mentioned design of the slab parts, reference mayalso be made to the illustration of such a slab part in FIG. 8.

To insert the slab parts 3 a, 3 b in pairs between the rails 2 of atrack, they may at first be arranged in the folded-up position and puttogether with their meander-like designed rims 26, 27, as is illustratedin FIG. 9, the elastic sections 5 of C-shaped cross-section also beingarranged between the carrying ribs 4 of the slab parts 3 a, 3 b and therails 2. Subsequently, the slab parts 3 a, 3 b are downwardly pivoted orfolded, as indicated by the arrow 35, until they assume the levelledposition illustrated in FIGS. 5 to 7, in which the slab parts 3 a, 3 bof each slab pair self-supportingly bridge the space 22 between therails 2.

The carrying surfaces 33 provided in the carrying portions 28 have acrowned shape, and such a crowned shape is also found on the restingsurfaces 34 provided on the resting portions 29, and by this crownedshape of the above-indicated surfaces, a positive locking of the slabparts 3 a, 3 b is provided which inhibits mutual movement of these slabparts in the direction of the slab plane (arrows 36) in the levelledposition of the slab parts 3 a, 3 b. Furthermore, projections 37 areprovided on the resting surfaces 34 and indentations 38 are provided onthe carrying surfaces 38, which are shaped complementary to theprojections 37; in the levelled position of the slab parts, theprojections 37 latchingly engage in the indentations 38 resulting in amutual latching of the slab parts 3 a, 3 b.

If desired, an elastic and/or shock-braking insert or coating can beprovided between the carrying surfaces 33 and the resting surfaces 34.

Originating from the rim 26 or 27 of the respective slab part 3 a or 3b, respectively, the carrying surfaces 33 provided on the carryingportions at first rise steeply, starting from the slab lower side 31,and then flatten, which is advantageous for assembling the slab parts toslab pairs. From the geometrical standpoint it is suitable if suchcrowned carrying surfaces are shaped like a toothing which allows for arelative sliding movement or rolling movement of the facing carryingsurfaces and resting surfaces one on the other, up to a levelledposition of the slab parts 3 a, 3 b of the respective slab pair, andwhich then, in the levelled position (FIGS. 5 to 7), locks these slabparts 3 a, 3 b against a movement relative to each other. This surfaceshape which geometrically corresponds to a toothing may extend as far asto the slab upper side 12.

The projections 37 may be provided at the front rims 39 of the restingportions 29, as is illustrated in FIGS. 5 to 8, as may be advantageouswhen assembling the slab parts; it is, however, also possible to mouldsuch projections 37 at a different location, e.g. at a slight distancefrom the rim of the resting surfaces.

In the modification illustrated in FIG. 10, the carrying surfaces 33 andthe resting surfaces 34 are configured to be largely plane; also in thisinstance, the indentations 38 in which the projections 37 engage areprovided for a mutual latching of the slab parts 3 a, 3 b.

Both in the embodiment illustrated in FIGS. 5 to 7 and in themodification illustrated in FIG. 10, the two slab parts 3 a, 3 b of aslab pair rest on each other to engage meander-like on the slab lowerside 31, so that the facing rims of the slab parts 3 a, 3 b extend tofollow a meander-like line 43 at the slab lower side. This results in avery intimate positive fit of the slab parts 3 a, 3 b which togetherform a slab pair.

Yet the design of the mutually contacting or engaging portions of theslab parts of a slab pair may also be chosen such that the facing rims26, 27 of the slab parts 3 a, 3 b abut each other at the slab lower side31 along a straight line 40, whereby both the production of the slabsand the course of the assembling procedure can be simplified; such adesign is present in the embodiments illustrated in FIGS. 11 to 16. Manydetails of these embodiments are analogous to those of the embodimentsof FIGS. 5 to 10, and therefore reference may be made in this connectionto the previous explanations relating to FIGS. 5 to 10. With theembodiment according to FIGS. 11 to 14, the carrying surfaces 33 have acrowned shape, while in the modification according to FIG. 16, thesecarrying surfaces 33 have a substantially plane configuration. In bothinstances, projections 37 engaging in indentations 38 are arranged atthe front rims of the resting portions. Yet, as has already beenmentioned above, such projections 37 may also be placed at differentlocations in the region of the resting surfaces.

In the embodiments illustrated in FIGS. 11 to 16, the slab parts 3 a, 3b are shaped to be rounded at their facing rims 26, 27 from the platelower side 31 upwards, the radius of curvature of this rounded portionbeing equally dimensioned or smaller than the distance 41 between therims 26, 27 and the rail-side rims 42 of the slab parts 3 a, 3 b. Alsothis measure is advantageous for as unimpeded a course of the insertionprocedure of the slab parts as possible.

According to a preferred embodiment it is provided that thereinforcement 11 provided in the slab parts extends over the entire areaof the slab parts 3 a, 3 b, reaching, as is indicated in broken lines inFIG. 8, both into the carrying portions 28 and resting portions 29 andinto the carrying ribs 4.

Also in the embodiments formed with the slab parts 3 a, 3 b, cavityresonators 14 including sound apertures 15 can be provided, as isillustrated, e.g., in FIGS. 11 to 14. Likewise, the slabs can also beprovided with frames 44, as is illustrated in broken lines, e.g., inFIG. 11.

What is claimed is:
 1. A noise control device for tracks comprisingsound absorbing slabs mounted at the rails of the track, the slabs beingsupported on the rails via elastic sections, and the slabs arrangedbetween the rails self-supportingly bridging the space between therails, characterized in that the slabs (3; 18; 21) are porous andcomprised lightweight building material combined by a binder and thatthe slabs (3; 18; 21) have a reinforcement (11).
 2. A noise controldevice according to claim 1, characterized in that the upper side (12)of the slabs (3; 18; 21) is structured.
 3. A noise control deviceaccording to claim 2, characterized in that the structuring isirregular.
 4. A noise control device according to claim 2, characterizedin that the upper side of the slabs (3; 18; 21) is provided with ribs(13) extending in parallel to the rails (2).
 5. A noise control deviceaccording to claim 4, characterized in that the ribs (13) have atrapezoidal cross-section.
 6. A noise control device according to claim1, characterized in that cavity resonators (14) having tubular soundapertures (15) directed to the upper side (12) of the slabs (3; 18; 21)are formed in the slabs (3).
 7. A noise control device according toclaim 6, characterized in that the walls of the cavity resonators (14)and their sound apertures (15) are provided with a silencingstructuring.
 8. A noise control device according to claim 6,characterized in that the walls of the cavity resonators (14) and theirtubular sound apertures (15) are provided with a silencing layer.
 9. Anoise control device according to claim 6, characterized in that thecavities forming the cavity resonators (14) are designed such that theywiden downwardly and are open, and are covered by a lower plate (16).10. A noise control device according to claim 6, characterized in thatthe cavities forming the cavity resonators (14) are designed such thatthey widen downwardly and are open and form a resonance cavity togetherwith the space present between the rail bedding (17) and the lower sideof the respective slab (3).
 11. A noise control device according toclaim 6, characterized in that the silenced resonance frequency of thecavity resonators (14) lies within a frequency range of from 150 to1,000 Hz, preferably between 500 and 1,000 Hz.
 12. A noise controldevice according to claim 1, characterized in that the space (22)present between the two rails (2) of a track (1) is bridged with slabparts (3 a, 3 b) arranged in pairs, each engaging by at least onecarrying rib (4) in the fishing surfaces (23) of the rails (2), the slabparts (3 a, 3 b) of each slab pair being supported on each other attheir facing rims (26, 27), carrying portions (28) and resting portions(29) alternatingly following each other in meander-like fashion at eachrespective slab part along the rim facing the other slab part, thecarrying portions being formed by indentations (30) originating from theslab upper side (12), which indentations extend as far as to the rimfacing the other slab part, upwardly directed indentations (32)originating from the slab lower side (31) being formed below the restingportions (29), which indentations are shaped complementary to theindentations of the carrying portions, and that the resting portions ofthe one slab part rest on the carrying portions of the other slab part,and that the resting portions of the other slab part rest on thecarrying portions of the one slab part.
 13. A noise control deviceaccording to claim 12, characterized in that at those surfaces (33, 34),on which the slab parts (3 a, 3 b) of one slab pair contact each other,projections (37) and indentations (38) shaped complementary to theprojections are formed, the projections latchingly engaging in theindentations for a mutual latching of the slab parts (3 a, 3 b).
 14. Anoise control device according to claim 12, characterized in that thecarrying surfaces (33) provided in the carrying portions (28),originating from the rim facing the other slab part of the slab pair, atfirst rise steeply, starting from the slab lower side (31), and thenflatten.
 15. A noise control device according to claim 14, characterizedin that the carrying surfaces (33) provided in the carrying portions(28) have a crowned shape, which shape inhibits a mutual movement of theslab parts (3 a, 3 b) in the direction of the slab plane (36) in thelevelled position of the slab parts (3 a, 3 b) of the respective slabpair.
 16. A noise control device according to claim 13, characterized inthat downwardly extending projections (37) are provided at the frontrims (39) of the resting portions (29) and indentations (38)complementary to these projections (37) are provided on the carryingsurfaces (33) of the carrying portions (28).
 17. A noise control deviceaccording to claim 15, characterized in that the crowned carryingsurfaces (33) are shaped like a toothing which allows for a slidingmovement or rolling movement of the facing carrying surfaces and restingsurfaces one on the other, up to a levelled position of the slab parts(3 a, 3 b) of the respective slab pair, and which in the levelledposition of these slab parts locks against a movement of these slabparts relative to each other.
 18. A noise control device according toclaim 12, characterized in that the slab parts (3 a, 3 b) are shaped tobe rounded at their facing rims (26, 27) from the plate lower side (31)upwards, the radius of curvature being equally dimensioned or smallerthan the distance (41) between these rims (26, 27) and the rail-siderims (42) of the slab parts (3 a, 3 b).
 19. A noise control deviceaccording to claim 12, characterized in that the two slab parts (3 a, 3b) of a slab pair abut each other at the slab lower side (31)approximately along a straight line (40).
 20. A noise control deviceaccording to claim 12, characterized in that the two slab parts (3 a, 3b) of a slab pair abut each other at the slab lower side (31) so as toengage each other in meander-like fashion.
 21. A noise control deviceaccording to claim 12, characterized in that the reinforcement (11)provided in the slab parts (3 a, 3 b) extends over the slab area (36)and reaches into the carrying portions (28) and resting portions (29) aswell as into the carrying ribs (4).
 22. A noise control device accordingto claim 12, characterized in that an elastic and/or shock-brakinginsert or coating is provided between the carrying surfaces (33)provided on the carrying portions and the resting surfaces (34) providedon the resting portions.
 23. A sound-absorbing slab for a noise controldevice according to claim 1, characterized in that the slab (3; 18; 21)is comprised of particles (9) of porous lightweight building materialcombined by a binder, that the slab (3; 18; 21) has an embeddedreinforcement (11), and that in the slab (3; 18; 21) cavity resonators(14) are formed with tubular sound apertures (15) oriented towards theone large surface of the slab (3; 18; 21), which large surface isintended to form the upper side when installing the slab in the track.24. A sound-absorbing slab according to claim 23, characterized in thatthe cavities forming the cavity resonators (14) are designed to widenand to be open towards that large surface which is located at that sideof the slab that faces away from the tubular sound apertures (15).
 25. Asound-absorbing slab according to claim 24, charaterized in that thecavities forming the cavity resonators (14) are covered by a lower plate(16) at the side facing away from the tubular sound apertures (15). 26.A sound absorbing slab for a noise control device according to claim 12,characterized in that the slab (3 a, 3 b) is comprised of particles ofporous lightweight building material combined by a binder, that the slab(3 a, 3 b) has an embedded reinforcement, that the slab (3 a, 3 b) onone rim side is provided with a carrying rib (4) for engagement in thefishing surfaces of rails and at the rim side opposite this carrying rib(4) comprises meander-like successive carrying portions (28) and restingportions (29), the carrying portions being formed by indentations (30)originating from the slab upper side (12) and extending as far as to therim, upwardly directed indentations (32) originating from the slab lowerside (31) being formed below the resting portions (29) and being shapedcomplementary to the indentations of the carrying portions.
 27. Asound-absorbing slab according to claim 26, characterized in that in theslab (3 a, 3 b) cavity resonators (14) are formed with tubular soundapertures (15) oriented towards the one large surface of the slab (3 a,3 b), which large surface is intended to form the upper side wheninstalling the slab in the track.
 28. A sound-absorbing slab accordingto claim 26, characterized in that the reinforcement (11) provided inthe slab (3 a, 3 b) extends over the entire slab area and into thecarrying portions (28) and into the resting portions (29) as well asinto the carrying rib (4).